Optical Disc Focal Point Detection Using Laser Interference
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Solution Overview
Problem
Existing optical drives face challenges in accurately determining whether the recording layer of an optical disc is at the focal point of the objective lens due to high-speed spinning, which affects data reading and writing, and current astigmatic methods are not precise enough.
Innovation Solution
A detection apparatus using a pulsed laser split into two beams by a beam splitter, where the interference signal from the overlapping beams is used to determine if the recording layer is at the focal point, independent of beam spot shape and symmetry, with a servo controller adjusting the optical disc's position for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the optical disc spins at high speed, then data reading and writing capability is improved, but the recording layer deviates from the focal point due to vibration
Solution Approach 1:
The patent implements a feedback mechanism where the detector continuously monitors the position of the recording layer relative to the focal point by analyzing the reflected laser beam. The servo controller receives this detection signal and automatically adjusts the objective lens position to compensate for vibrations caused by high-speed disc rotation, ensuring the recording layer remains at the focal point for accurate data reading and writing
Solution Approach 2:
The patent replaces mechanical vibration damping methods with an optical detection and electronic control system. Instead of mechanically stabilizing the disc or lens, the system uses laser beam reflection detection and servo control to achieve focal point alignment, enabling high-speed rotation without mechanical interference
2Device complexity
If the astigmatic method is used to detect focal point alignment, then the detection process is simplified, but high requirements are posed on beam spot shape and symmetry
Solution Approach 1:
The patent changes the detection parameter from beam spot shape analysis to optical path difference measurement. By measuring the difference in optical path lengths between reference and detection beams, the system determines focal point alignment without relying on beam spot symmetry, thereby improving measurement precision while maintaining simplified detection process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides high precision in determining the focal point alignment, enabling accurate data reading and writing by moving the optical disc to the focal point with micron-level precision, improving detection accuracy and reducing vibrations' impact.
Implementation Method 1
The beam splitter is configured to receive an incident pulsed laser whose propagation direction is parallel to the optical axis of the objective lens, and split the incident pulsed laser into a first beam and a second beam
Implementation Method 2
The reflector is configured to receive the first beam, and obtain a third beam through reflection based on the first beam
Implementation Method 3
The objective lens is configured to receive the second beam, focus the second beam on an optical disc
Implementation Method 4
transmit a fourth beam reflected by the optical disc based on the second beam
Implementation Method 5
The detector is configured to obtain an interference beam from the third beam transmitted by the beam splitter and the fourth beam reflected by the beam splitter
Implementation Method 6
The detector is configured to obtain an interference beam from the third beam transmitted by the beam splitter and the fourth beam reflected by the beam splitter, determine an interference signal of the interference beam
Data Source
AI summary
A detection apparatus determines whether a recording layer of an optical disc is at a focal point of an objective lens. The detection apparatus includes an objective lens, a beam splitter, a reflector, a detector, and a servo controller. The reflector and the detector are disposed opposite to each other on two sides of an optical axis of the objective lens, and a normal line of the reflector is perpendicular to the optical axis. The beam splitter is disposed between the reflector and the detector and is located on the optical axis. The servo controller is connected to the detector.